The present invention generally relates to wireless communication networks, and particularly relates to load balancing in wireless packet data networks.
Current and evolving wireless communication networks offer a range of packet data services. The push toward higher data rates led to the introduction of shared, high-speed packet data channels in several of the current wireless communication network standards. The IS-2000 standards for cdma2000 networks introduced the high-rate Forward Packet Data Channel (F-PDCH), for example, and the W-CDMA standards introduced the High Speed Downlink Packet Access (HSDPA) channel.
Several subscribers (mobile stations) simultaneously share a F-PDCH (or HSDPA channel), and each one is served on the channel via time-multiplexed delivery of per-subscriber data. Some form of “scheduler” manages the multiplexed delivery of data according to one or more service criteria, such as by prioritizing delivery to subscribers in good radio conditions with maximum throughput as the scheduling goal, or by prioritizing delivery to subscribers that are underserved relative to their prevailing radio conditions with “fairness” of service as the scheduling goal.
In a typical cdma2000-based network offering F-PDCH services, each radio sector transmits the F-PDCH, and individual mobile stations are served on the F-PDCH in the radio sector that currently provides the “best” signal quality. Each mobile station dynamically monitors the signal quality from its serving sector and from the other sectors in its “active set” of radio sectors that are candidates for serving it on the F-PDCH.
If the signal quality from one of the candidate sectors becomes better than that of its current serving sector, the mobile station selects that candidate sector as its new serving sector and signals that reselection to the network. In turn, the base station controller or other entity managing the involved radio sectors coordinates the transfer of that mobile station's packet data traffic from the F-PDCH of the old serving sector to the F-PDCH of the new serving sector.
Mobile stations receiving packet data traffic the F-PDCH thus “move” toward the best signal strength and, ultimately, end up selecting the radio sector offering them the best signal strength. Of course, the radio sector offering the best signal strength to a given mobile station is not always the best F-PDCH serving sector for that mobile station.
Indeed, the F-PDCH in that sector already may be heavily loaded, or there may be a relatively large number of dedicated channel users operating in that sector—mobile stations engaged in circuit-switched voice or low-rate data services—which reduces the transmit power and spreading code availability for the F-PDCH. In short, mobile stations autonomously selecting and reselecting serving sectors for F-PDCH service based simply on following the best radio sector signal strength leave the supporting wireless packet data network vulnerable to potentially significant congestion and efficiency problems.